Method of redirecting I/O operations to memory

ABSTRACT

A computer system is described in which a table created in memory includes drive description data for one or more IDE devices included in the system. A command intercept circuit is described which intercepts device-identification commands and reroutes the device-identification operation to memory. The command intercept circuit includes an address decode circuit which asserts a first control signal upon decoding an address corresponding with the one or more IDE devices. A command decode circuit responds to the asserted first control signal to decode data and asserts a second control signal when the decoded data corresponds with a device-identification command. An address generator responds to the asserted second control signal to generate a memory address where the drive description data table is stored.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 08/756,171, filed Nov. 25, 1996 still pending.

TECHNICAL FIELD

This invention relates generally to operating computer systems, and more particularly, to a method for identifying data storage devices used in computer systems.

BACKGROUND OF THE INVENTION

The use of computers, especially personal computers (PCs) is widespread. The computing power of the PC, whether coupled to a network or operating as a stand-alone device, has increased significantly as new computer designs move into production. Central processing units have become faster and more complex with each new generation of PC. Memory chips have also increased in both capacity and speed. Other elements, such as disk drives and compact disk read-only memory drives are common on PCs.

As the new computer designs have consistently increased computing power, the complexity of the programs that run the computer has correspondingly increased. To take advantage of the increased computing power, operating systems, such as Microsoft MSDOS® and Microsoft Windows® 95, have become more complex. As a result, the installation and set-up of a new computer can be extremely complex, especially for individuals with little or no technical training.

Certain computer devices, such as integrated device electronics (IDE) devices and "plug and play" interface boards, have the ability to be identified by the computer operating system and/or other system management software, which is then configured accordingly. But while the speed of central processing units and memories have increased, there are limitations to the speed at which the IDE devices can transfer data, including data used to identify the devices. For example, writing an auto-identification command to an IDE disk drive is slow relative to the processing speed of the central processing unit, as is reading drive-identifying data retrieved from the IDE disk drive. Further, currently available schemes for managing multiple drive systems and/or protecting regions on a drive that might otherwise be used by system management software are awkwardly implemented and result in sub-optimal system performance. Therefore, it can be appreciated that there is a significant need for an improved system and method for identification of computer data storage devices. The present invention provides this and other advantages as will be apparent from the following detailed description and accompanying figures.

SUMMARY OF THE INVENTION

According to the present invention, a computer system is provided in which a table created in memory includes device description data for one or more I/O devices included in the system. The device description data is first transferred to memory during initialization of the computer system. Once stored in memory, the device description data can be modified and/or combined with other device description data to produce a "virtual" device description data table. Subsequent device-identification commands are then intercepted and the "virtual" device description data retrieved.

A command intercept circuit is described which intercepts the device-identification commands and reroutes the device-identification operation to memory. The command intercept circuit includes an address decode circuit which asserts a first control signal upon decoding an address corresponding with the one or more IDE devices. A command decode circuit responds to the asserted first control signal to decode data and asserts a second control signal when the decoded data corresponds with a device-identification command. An address generator responds to the asserted second control signal to generate a memory address where the drive description data table is stored.

A computer system, according to the present invention, includes a processor and a memory for storing data at locations addressable by the processor. An I/O device is provided which is addressable by the processor and transfers data to and from the processor. A system controller couples the memory with the processor, as well as the I/O device with the processor, and controls the transfer of data and address information between the memory and the processor, as well as between the I/O device and the processor. The command intercept circuit is coupled with the processor and with the memory. The command intercept circuit selectively intercepts certain data transfer operations addressed by the processor to the I/O device and reroutes these operations to the memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a computer system having a system controller according to the present invention.

FIG. 2 is a functional block diagram of a portion of the system controller of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

A novel system and method is described for identifying data storage devices used in computer systems. In the following description, specific details are set forth in order to provide a sufficient understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced without these details. In other instances, well-known circuits, control signals and timing protocols have not been shown in detail in order not to unnecessarily obscure the invention.

FIG. 1 shows a computer system 40, such as an IBM compatible personal computer, according to the present invention. A microprocessor 50, such as the Pentium™ processor, is connected to a processor bus 52 which carries address, data and control signals. The processor bus 52 is in turn connected to a system controller 54 and a cache memory 53, such as a static random access memory (SRAM) array. The system controller 54 acts as a memory controller accessing a main memory, such as a system dynamic random access memory (DRAM) 56, via a memory bus 58 which carries address, data and control signals. The system DRAM 56 can include any of various known memory devices, such as DRAM devices manufactured by Micron Technology, Inc.

The system controller 54 also serves as a bridge circuit between the processor bus 52 and an expansion or I/O bus 62. The I/O bus 62 may itself be a combination of one or more bus systems with associated interface circuitry (e.g., PCI bus with connected SCSI and ISA bus systems). Connected to the I/O bus 62 are multiple I/O devices 64-68. One or more data input devices 64, such as a keyboard, mouse, etc., are coupled to the I/O bus 62. Similarly, one or more data output devices 65, such as visual display devices, printers, etc., are coupled to the I/O bus 62. Also coupled to the I/O bus 62 are integrated device electronics (IDE) devices 66-68, together with associated IDE controllers 66A-68A. Included are hard drives 67 and 68, and a generic IDE device 66 representing one or more additional IDE devices, such as tape drives, CD-ROM drives, or additional hard drives. It should be understood that some IDE devices can share a common controller. For example, the hard drives 67, 68 and the generic IDE device 66 could all be controlled by a single enhanced-IDE (EIDE) controller instead of the separate IDE controllers 66A-68A illustrated in FIG. 1. IDE devices are well known to those skilled in the art, and need not be discussed in detail.

A read-only memory basic input/output system (ROM BIOS) 70 is coupled to the I/O bus 62 and provides various well-known instruction sets to the microprocessor 50. Included are the start-up routines for power-on self-test (POST), system configuration initialization and disk boot (in which a computer operating system program is located and instructions therefrom executed by the microprocessor 50). The ROM BIOS 70 also includes hardware interrupt handling and program service request handling routines. The program service request handling routines attend to the details of interacting with I/O devices and service those requests initiated by software programs to, for example, read information from a hard drive, clear a display screen, or write information to a printer. The hardware interrupt handling routines handle requests initiated by hardware components of the computer system, such as when a key is pressed on a keyboard.

Under control of instructions provided by the BIOS 70, the microprocessor 50 initializes various system components by checking for system configuration information (typically stored in a battery powered CMOS memory) and/or electronically interrogating the system components and checking for a response. One such interrogation is the well-known "Identify Drive" command, to which the IDE devices 66-68 respond by providing drive description data, which typically includes the drive manufacturer, performance capabilities, geometry of the drive, etc. A typical response from one of the hard drives 67, 68 is illustrated below in Table 1.

                                      TABLE 1                                      __________________________________________________________________________     DATA FORMAT:                                                                   __________________________________________________________________________     Word Bit 7/15                                                                            Bit 6/14                                                                              Bit 5/13                                                                              Bit 4/12                                                                            Bit 3/11                                                                             Bit 2/10                                                                             Bit 1/9                                                                              Bit 0/8                         mvl = 1   CMD PKT DRQ = 01b                                                                            0    0     0     P Size = 00b                          0    Protocol = 10b                                                                             Device Type = 000101b                                         1 ... 9                                                                             Not used or reserved = all zero                                           10 ... 19                                                                           Serial Number = all zero (Not supported)                                  20   Buffer Type = 0000h (Not supported)                                       21   Transfer Size = 0080h (128KBytes) {FX001DEFXN01DE} = 0100h                     (256Kbytes) {FX002DEFXN02DE}                                              22   Not used = 0000h                                                          23 ... 26                                                                           Firmware Version = E???                                                   27 ... 46                                                                           Model Number = `FX001DE` = `FXN01DE` = `FX002DE` = `FXN02DE`              47   Not used = 000h                                                           48   Double Word I/O = 0000h (Not supported)                                        Vendor Unique = 00h                                                       49   0    0      0      0    IORDY=0                                                                              PRG=0 LBA=10                                                                               DMA=0                           50   Reserved = 0000h                                                          51   PIO Cycle Timing = 0000h (Mode 0) {FX001DE} = 0200h (Mode 2)                   {FX002DE}                                                                 52   DMA Cycle Timing = 0000h (Not supported)                                  53 ... 61                                                                           Not used = all zero                                                       62   Singleword DMA Mode=0000h (Not supported)                                 63   Multiword DMA Mode = 0000h (Not supported)                                64   Enhanced PIO Mode (Mode 3) = 0000h (Not supported)                        65   Blind PIO minimum cycle time = 0000h (Not supported)                      66   Recommended Multiword DMA Cycle Time = 0000h (Not supported)              67   Minimum PIO Cycle Time without Flow Control = 024Dh (589ns)                    {FX001DE} = 00EAh (234ns) {FX002DE}                                       68   Minimum PIO Cycle Time with IORDY = 0000h                                 69 ... 255                                                                          Reserved=all zero                                                         __________________________________________________________________________

In accordance with the present invention, this drive description data is transferred to the system DRAM 56 for storage therein. Preferably, the BIOS 70 routines cause the microprocessor 50 to initiate a direct memory access (DMA) transfer of the drive description data from each of the IDE devices 66-68 to the system DRAM 56. Alternatively, a programmed I/O or interrupt-driven I/O transfer of the drive description data is acceptable. Once stored in the system DRANM 56, the drive description data of the IDE devices 66-68 can be manipulated under software control, and a modified or "virtual" drive description data set is created which differs from the drive description data associated with the "actual" drive(s) employed.

One advantage of creating such a virtual drive is that certain storage regions of an actual drive can be protected from access by a computer operating system, system utilities and/or application software. Another advantage is that a plurality of actual drives can be logically combined to appear to the computer operating system, system utilities and/or application software as a single virtual drive. Similarly, an appropriate set of drive description data for a single virtual drive can be created for systems in which data is striped amongst multiple drives under hardware control, such as the well-known RAID (redundant array of independent disks) scheme. Those skilled in the art will appreciate additional advantages associated with the software definition of virtual drive parameters.

Once POST and system initialization are complete, the BIOS 70 routines cause the microprocessor 50 to retrieve and start a computer operating system program, such as MSDOS®. In particular, instructions within the BIOS 70 transfer control of the microprocessor 50 to a file within MSDOS called IO.SYS. The IO.SYS file further initializes the computer system 40 in a well-known manner and also loads a data file called CONFIG.SYS which configures hardware and software for proper operation. For example, the system DRAM 56 can be configured to reserve space for certain application programs, the number of I/O channels and buffer sizes are selected, and certain software routines (known as drivers) for accessing I/O devices are loaded into the system DRAM. The operation of the files IO.SYS and CONFIG.SYS are well known to those skilled in the art, and need not be discussed in detail. Computer operating systems other than MSDOS have similar files with similar functional characteristics.

In particular, the computer operating system loads software drivers for the IDE devices 66-68 into the system DRAM 56. As part of the hardware and software initialization/configuration, the computer operating system may cause the microprocessor 50 to initiate an I/O cycle and issue the "Identify Drive" command for one or more of the IDE devices 66-68. In accordance with the present invention, this command is intercepted and the I/O cycle is rerouted to a memory cycle accessing the virtual drive description data stored in the system DRAM 56. Similarly, any application software routines which attempt to access the drive description data associated with one or more of the IDE devices 66-68 will receive the virtual drive description data stored in the system DRAM 56.

FIG. 2 shows a portion of the system controller 54 of FIG. 1 which intercepts and reroutes the "Identify Drive" I/O command. In order not to unnecessarily obscure the invention, other portions of the system controller 54 are onitted, and only those interconnections necessary to describe the invention are included. The address, data and control portions of the processor bus 52 of FIG. 1 are shown individually as the address bus 52A, data bus 52B and control bus 52C, respectively. Similarly, the address, data and control portions of the memory bus 58 of FIG. 1 are shown individually as the memory address bus 58A, memory data bus 58B and memory control bus 58C, respectively.

A memory control state machine 80 receives control signals from the processor 50 (see FIG. 1) on the control bus 52C. These control signals are well known and include those identifying the status of the address bus 52A, defining bus cycle types (e.g., memory read or write, I/O read or write), arbitrating bus ownership, and controlling burst cycles. The memory control state machine 80 in turn issues signals controlling the functioning of the system DRAM 56 on the memory control bus 58C. Well-known memory control signals include row address strobe (RAS), column address strobe (CAS), write enable (WE) and output enable (OE). The memory control state machine 80 receives a clock signal CLK, which may be the system clock signal received by the microprocessor 50, and controls the timing of data transfer between the processor data bus 52B and the memory data bus 58B via a data path register/transceiver 82.

During execution of the system configuration initialization routines stored within the BIOS 70, a control register 84 is programmed with values which effect the functions of the system controller 54. An address decode circuit 86 receives address information on the address bus 52A and controls registration of data provided on the data bus 52B in the control register 84. When the "Identify Drive" command intercept function is employed, values programmed in the control register 84 produce an intercept enable signal which is input to the memory control state machine 80 and enables control circuitry therein (not shown) to produce corresponding control signals described below. Also, comparison data is written to the address decode circuit 86 and a command decode circuit 90, allowing these circuits to subsequently recognize IDE addresses and the "Identify Drive" command, respectively. Additional details concerning the programming of the control register 84 and corresponding effects on system functions are well known to those skilled in the art, and need not be discussed in detail.

Also included in the command intercept circuitry are a command latch circuit 88, an address generator 92, and an address multiplexer 94. When one of the IDE devices 66-68 of FIG. 1 is addressed, the address decode circuit 86 asserts a control signal which latches the contents of the data bus 52B in the command latch circuit 88. The command latch circuit 88 provides the latched data to the command decode circuit 90. The address decode circuit 86 also asserts an IDE signal to the memory control state machine 80, indicating that an I/O operation to an IDE device has begun. If the data latched in the command latch circuit 88 corresponds to an "Identify Drive" command, the command decode circuit 90 asserts a control signal to activate the control circuitry within the memory control state machine 80. In turn, the memory control state machine 80 asserts an activation control signal to cause the address generator 92 to produce address information corresponding to the location of the virtual drive description data stored in the system DRAM 56. The memory control state machine 80 also produces a mux select signal causing the address mux 94 to pass the output of the address generator 92 to the memory address bus 58A. The address generator 92 includes a base address register (not shown), which is programmed during system initialization, and a counter (not shown) for generating a series of addresses sufficient to access the entire virtual drive description data set stored in the system DRAM 56.

In the event of a regular memory access, the address decode circuit 86 asserts a memory signal to the memory control state machine 80, indicating that the address carried on the address bus 52A is for a location in the system DRAM 56. The control signals produced by the address decode circuit 86 and the command decode circuit 90 are deasserted, and the memory control state machine 80 issues a mux select signal causing the address mux 94 to pass the contents of the address bus 52A to the memory address bus 58A The memory cycle then continues according to conventional protocols.

Each of the circuits whose function and interconnection is described above in connection with FIGS. 1 and 2 is of a type known in the art, and one skilled in the art would be able to use such circuits in the described combination to practice the present invention. The internal details of these particular circuits are not part of, nor critical to, the invention. Therefore, a detailed description of the internal circuit operation is not required. Similarly, details of software manipulation of the actual drive description data set(s) to create virtual drive description data set(s) is not described.

It will be appreciated that, although an embodiment of the invention has been described above for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Those skilled in the art will appreciate that any number of well-known processor, system controller and bus types could be employed according to the present invention. Also, the IDE command intercept circuitry need not be integrated within the system controller, although it is preferable to do so. Additionally, one or more of the circuits within the command intercept circuitry could be omitted, such as the command latch circuit 88, or have its function integrated into others of the described circuits. Further, certain control signals could be routed differently, such as the control signal produced by the command decode circuit 90 being provided directly to the address generator 92 and/or the address mux 94.

Those skilled in the art will also appreciate that certain of the IDE devices contained within a computer system may be subject to the virtual drive creation and auto-identification intercept function, whereas other IDE devices are not. Additionally, the present invention applies to any device which provides device-identifying data in response to an auto-identification command, and not just the particular IDE-type devices described. Indeed, numerous variations are well within the scope of this invention. Accordingly, the invention is not limited except as by the appended claims. 

I claim:
 1. In a computer circuit having a processor, a memory for storing data at locations addressable by the processor, and an I/O device addressable by the processor and operable to transfer data to and from the processor, a method of redirecting a data transfer operation addressed to the I/O device, comprising the steps of:receiving a first address provided by the processor and producing a first control signal in response thereto, the first control signal having an asserted state when the first address corresponds with the I/O device; in response to the asserted state of the first control signal, decoding data provided by the processor and producing a second control signal in response thereto, the second control signal having an asserted state when the decoded data corresponds to a first I/O command; in response to an asserted state of the second control signal, generating a second address corresponding with the first address; and providing the second address to the memory.
 2. The method of claim 1, further comprising the steps of:in response to a deasserted state of the second control signal, providing the first address to the memory.
 3. The method of claim 1, further comprising the steps of:in response to a deasserted state of the first control signal, providing the first address to the memory.
 4. In a computer circuit having a processor, a memory for storing data at locations addressable by the processor, and an I/O device addressable by the processor and operable to transfer data to and from the processor, a method of identifying the I/O device, comprising the steps of:issuing an auto-identification command to the I/O device; retrieving device-identifying data set from the I/O device; transferring the device-identifying data from the I/O device to the memory; modifying the device-identifying data stored in the memory; and intercepting a subsequent auto-identification command to the I/O device and retrieving the modified device identifying data from the memory.
 5. The method of claim 4, wherein the step of intercepting a subsequent auto-identification command comprises the steps of:receiving a first address provided by the processor and producing a first control signal in response thereto, the first control signal having an asselted state when the first address corresponds with the I/O device; in response to the asserted state of the first control signal, decoding data provided by the processor and producing a second control signal in response thereto, the second control signal having an asserted state when the decoded data corresponds to the auto-identification command; in response to an asserted state of the second control signal, generating a second address corresponding with the first address; and providing the second address to the memory.
 6. The method of claim 1 wherein the first I/O command is an auto-identification command.
 7. In a computer system having a processor, a memory for storing data at locations addressable by the processor, and a plurality of I/O devices addressable by the processor and operable to transfer data to or from the processor, the I/O devices including a first I/O device operable to provide device-identifying data in response to an auto-identification command, a method of controlling data transfer operations addressed to the I/O devices, comprising:receiving an I/O address; determining if the I/O address corresponds to the first I/O device; receiving an I/O command; determining if the I/O command is the auto-identification command; if the I/O address corresponds to the first I/O device and the I/O command is the auto-identification command, then producing a memory address corresponding to the I/O address; and providing the memory address to the memory.
 8. The method of claim 7 wherein the first I/O device is an IDE device.
 9. The method of claim 7 wherein determining if the I/O address corresponds to the first I/O device includes comparing the I/O address to previously stored address data.
 10. The method of claim 7 wherein determining if the I/O command is the auto-identification command includes comparing the I/O command to previously stored command data. 